The interactions among higher cells play a profound role in normal development and maintenance of homeostasis in multicellular organisms. Abnormal growth is often associated with the loss of normal cell interactions. The myxobacteria are unique among the procaryotes in manifesting a variety of organized cell-cell interactions. These pervade the entire cycle of development; they include swarming, chemotactic aggregation and fruiting body formation; communication among germinating myxospores and coordinated growth and DNA synthesis during germination and outgrowth. We plan to investigate in detail aggregation and the nature, regulation, perception and response to a specific, auto- signal for germination. We hope that the study of these cell interactions in a developing procaryotic system will serve as an additional model for understanding the more complicated communal activity among higher cells.